The instant application relates to a process for the operation of an open-end spinning device.
It is known from the state of the art that open-end rotor spinning machines are equipped with a travelling service unit which is able to eliminate malfunctions at spinning stations autonomously. Such a device is described in DE 32 02 428 A1, for example. The service unit becomes active, for example to exchange fully wound bobbins against empty tubes. However, the utilization of the service unit to eliminate malfunctions in yarn production is its special area of application. A service unit patrolling alongside the spinning stations of the rotor spinning machine which communicates with a machine center as it passes the spinning stations and is informed on the state of the spinning station by the machine center is known through the RU 14 open-end spinning machine of Schubert & Salzer Maschinenfabrik Aktiengesellschaft, now Rieter Ingolstadt Spinnereimaschinenbau AG 85046 Ingolstadt/Germany. When the service unit arrives at a spinning station having a malfunction, caused for example by yarn breakage, the service unit becomes automatically active and starts to set the yarn production at the spinning station in motion again. Aside from stoppages which cannot be corrected by the service unit, yarn breakage is the most important source of malfunction. It is caused through dirt in the rotor for instance, so that the continuous yarn production can no longer be maintained, resulting in the breaking of the yarn and stoppage of the spinning station. In the known rotor spinning machines, a stopping of the spinning station does however not mean that the spinning rotor is stopped, but only that the fiber feed to the spinning rotor is interrupted. The spinning rotor remains in its mounting and is driven by its tangential drive belt, thus ensuring constant conditions for the drive belt and for the adjoining spinning stations. If the service unit has reached a spinning station where yarn production is to be set again in motion, it assumes its position at this spinning station and attempts to set yarn production in motion again.
The individual steps of piecing are sufficiently known from the state of the art and shall be indicated only briefly here. The start-up of the spinning station begins, for example in the above-mentioned RU 14, with the search for the yarn end which is located on the partially wound bobbin. When the yarn end has been found it is prepared by the service unit and is fed back into the spinning rotor for the piecing of the new fibers to the yarn end. Following the twisting of the new fibers to incorporate them into the yarn, the yarn is withdrawn from the spinning device and is wound on the bobbin. The service unit thereupon transfers the yarn to the rotor spinning machine which takes over the further yarn production. The cleaning of the spinning rotor before the yarn end is fed back into it is an important activity of the service unit during this piecing of the yarn. To clean the rotor, the greatest variety of processes are used, e.g. pneumatic cleaning, cleaning by means of scrapers and cleaning by means of cleaning fluids.
As a rule, yarn production is resumed by the spinning station after the very first piecing attempt. It may however occur that a renewed attempt to restart the spinning station is necessary. In such case the sequence of steps for the piecing of the yarn begin again from the start. As a rule, a maximum of 3 attempts is made. If the spinning station has not been restarted after that, it is placed on malfunction status. This means that the machine center calls off the service unit from the spinning station, or that the service unit leaves the spinning station automatically. At the same time however, provisions are made so that the automatic service unit no longer services this spinning station as it passes it again on its patrol. It is then said that the spinning station has been shut down. However, this does not mean that the rotor of the spinning station is stopped, just as it is not stopped when a yarn breakage is caused by operation, but only means that the conveying of new fibers to the spinning rotor is interrupted. The rotor itself continues to run at operating speed and thereby affects the wear parts of the spinning station, such as the rotor bearing for example.
The known processes have therefore the disadvantage that the spinning station is under particular heavy stress, in particular the rotor bearing in radial and axial direction, because when the spinning station in which the rotor continues to run at operating speed is shut down, fibers or fiber remnants are as a rule present in the yarn-forming groove of the spinning rotor. In the worst case, these fibers or fiber remnants may result in a great imbalance of the rotor. This may lead to different types of damage to the rotor bearing and also to the spinning device. This is because the rotor movement becomes very unsteady and may begin to oscillate in radial direction. These oscillations produce a more or less extreme pressure against the supporting disks which produce an axial thrust, causing the rotor to be subjected axially to a force which will either damage the axial bearing of the rotor or will cause the rotor to be thrown in a counter-reaction from the axial bearing in the direction of the rotor cover.
The higher the rotational speed, the greater will be the effect of imbalance of the rotor, so that an improvement is important, in particular for rotor spinning devices running at high rotational speeds.